I think handwritten letters and postcards are still the best way to keep in touch with friends. I've always loved receiving them from my Lola and my friends abroad but it's even more exciting when you're the one sending them yourself. Stamp-picking is fun guys!
Snail mail is always a lovely way to make the people you miss most know that they're special and that the friendship you have with them is still intact despite the distance. *cues dramatic music*